Polarization-modulating element, illumination optical apparatus, exposure apparatus, and exposure method

ABSTRACT

There is disclosed a polarization-modulating element for modulating a polarization state of incident light into a predetermined polarization state, the polarization-modulating element being made of an optical material with optical activity and having a circumferentially varying thickness profile.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of application Ser. No. 13/067,958 filed Jul. 11,2011, which is a Continuation of application Ser. No. 12/461,801 filedAug. 25, 2009, which is a Continuation of application Ser. No.11/347,421 filed Feb. 6, 2006, which is a Continuation-In-Part ofApplication No. PCT/JP2005/000407 filed on Jan. 14, 2005. Thedisclosures of the prior applications are hereby incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polarization-modulating element,illumination optical apparatus, exposure apparatus, and exposure methodand, more particularly, to an exposure apparatus for production ofmicrodevices such as semiconductor elements, image pickup elements,liquid crystal display elements, and thin-film magnetic heads bylithography.

2. Related Background Art

In the typical exposure apparatus of this type, a beam emitted from alight source travels through a fly's eye lens as an optical integratorto form a secondary light source as a substantial surface illuminantconsisting of a number of light sources. Beams from the secondary lightsource (generally, an illumination pupil distribution formed on or nearan illumination pupil of the illumination optical apparatus) are limitedthrough an aperture stop disposed near the rear focal plane of the fly'seye lens and then enter a condenser lens.

The beams condensed by the condenser lens superposedly illuminate a maskon which a predetermined pattern is formed. The light passing throughthe pattern of the mask is focused on a wafer through a projectionoptical system. In this manner, the mask pattern is projected forexposure (or transcribed) onto the wafer. The pattern formed on the maskis a highly integrated pattern, and, in order to accurately transcribethis fine pattern onto the wafer, it is indispensable to obtain auniform illuminance distribution on the wafer.

For example, Japanese Patent No. 3246615 owned by the same Applicant ofthe present application discloses the following technology for realizingthe illumination condition suitable for faithful transcription of thefine pattern in arbitrary directions: the secondary light source isformed in an annular shape on the rear focal plane of the fly's eye lensand the beams passing the secondary light source of the annular shapeare set to be in a linearly polarized state with a direction ofpolarization along the circumferential direction thereof (hereinafterreferred to as a “azimuthal polarization state”).

SUMMARY OF THE INVENTION

An object of the embodiment is to transform incident light in a linearlypolarized state having a direction of polarization virtually along asingle direction, into light in a azimuthal polarization state having adirection of polarization virtually along a circumferential direction,while suppressing the loss of light quantity.

Another object of the embodiment is to form an illumination pupildistribution of an annular shape in a azimuthal polarization state whilewell suppressing the loss of light quantity, using apolarization-modulating element capable of transforming incident lightin a linearly polarized state having a direction of polarizationvirtually along a single direction, into light in a azimuthalpolarization state having a direction of polarization virtually along acircumferential direction.

Another object of the embodiment is to transcribe a fine pattern underan appropriate illumination condition faithfully and with highthroughput, using an illumination optical apparatus capable of formingan illumination pupil distribution of an annular shape in a azimuthalpolarization state while well suppressing the loss of light quantity.

In order to achieve the above objects, a first aspect of the embodimentis to provide a polarization-modulating element for modulating apolarization state of incident light into a predetermined polarizationstate,

the polarization-modulating element being made of an optical materialwith optical activity and having a circumferentially varying thicknessprofile.

A second aspect of the embodiment is to provide an illumination opticalapparatus comprising a light source for supplying illumination light,and the polarization-modulating element of the first aspect disposed inan optical path between the light source and a surface to beilluminated.

A third aspect of the embodiment is to provide an illumination opticalapparatus for illuminating a surface to be illuminated, based onillumination light supplied from a light source,

the illumination optical apparatus satisfying the following relations:RSP _(h)(Ave)>70%, and RSP _(v)(Ave)>70%,where RSP_(h)(Ave) is an average specific polarization rate aboutpolarization in a first direction in a predetermined effective lightsource region in a light intensity distribution formed in anillumination pupil plane of the illumination optical apparatus or in aplane conjugate with the illumination pupil plane, and RSP_(v)(Ave) isan average specific polarization rate about polarization in a seconddirection in the predetermined effective light source region.

The average specific polarization rates above are defined as follows:RSP _(h)(Ave)=Ix(Ave)/(Ix+Iy)AveRSP _(v)(Ave)=Iy(Ave)/(Ix+Iy)Ave.In the above equations, Ix(Ave) represents an average intensity of apolarization component in the first direction in a bundle of rayspassing through the predetermined effective light source region andarriving at a point on an image plane, Iy(Ave) an average intensity of apolarization component in the second direction in a bundle of rayspassing through the predetermined effective light source region andarriving at a point on the image plane, and (Ix+Iy)Ave an averageintensity of an entire beam passing through the predetermined effectivelight source region. The illumination pupil plane of the illuminationoptical apparatus can be defined as a plane in the optical relation ofFourier transform with the surface to be illuminated and, where theillumination optical apparatus is combined with a projection opticalsystem, it can be defined as a plane in the illumination opticalapparatus optically conjugate with an aperture stop of the projectionoptical system. The plane conjugate with the illumination pupil plane ofthe illumination optical apparatus is not limited to a plane in theillumination optical apparatus, but, for example, in a case where theillumination optical apparatus is combined with a projection opticalsystem, it may be a plane in the projection optical system, or may be aplane in a polarization measuring device for measuring a polarizationstate in the illumination optical apparatus (or in the projectionexposure apparatus).

A fourth aspect of the embodiment is to provide an exposure apparatuscomprising the illumination optical apparatus of the second aspect orthe third aspect, the exposure apparatus projecting a pattern onto aphotosensitive substrate through the illumination optical apparatus.

A fifth aspect of the embodiment is to provide an exposure method ofprojecting a pattern onto a photosensitive substrate, using theillumination optical apparatus of the second aspect or the third aspect.

A sixth aspect of the embodiment is to provide a production method of apolarization-modulating element for modulating a polarization state ofincident light into a predetermined polarization state, comprising:

a step of preparing an optical material with optical activity; and

a step of providing the optical material with a circumferentiallyvarying thickness profile.

The polarization-modulating element of the embodiment is made of theoptical material with optical activity, for example, like crystallinequartz, and has the circumferentially varying thickness profile. Thethickness profile herein is set, for example, so that light in alinearly polarized state having a direction of polarization virtuallyalong a single direction is transformed into light in a azimuthalpolarization state having a direction of polarization virtually alongthe circumferential direction. In consequence, the embodiment realizesthe polarization-modulating element capable of transforming the incidentlight in the linearly polarized state having the direction ofpolarization virtually along a single direction, into light in theazimuthal polarization state having the direction of polarizationvirtually along the circumferential direction, while suppressing theloss of light quantity. Particularly, since the polarization-modulatingelement is made of the optical material with optical activity, theinvention has the advantage that the polarization-modulating element isextremely easy to produce, for example, as compared with wave plates.

Therefore, since the illumination optical apparatus of the embodimentuses the polarization-modulating element capable of transforming theincident light in the linearly polarized state having the direction ofpolarization virtually along a single direction, into the light in theazimuthal polarization state having the direction of polarizationvirtually along the circumferential direction, it is able to form anillumination pupil distribution of an annular shape in the azimuthalpolarization state while well suppressing the loss of light quantity.Since the exposure apparatus and exposure method of the embodiment usethe illumination optical apparatus capable of forming the illuminationpupil distribution of the annular shape in the azimuthal polarizationstate while well suppressing the loss of light quantity, they are ableto transcribe a fine pattern under an appropriate illumination conditionfaithfully and with high throughput and, eventually, to produce gooddevices with high throughput.

The embodiment will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the embodiment.

Further scope of applicability of the embodiment will become apparentfrom the detailed description given hereinafter. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will be apparent to those skilled inthe art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration schematically showing a configuration of anexposure apparatus according to an embodiment of the present invention.

FIG. 2 is an illustration to illustrate the action of a conical axiconsystem on a secondary light source of an annular shape.

FIG. 3 is an illustration to illustrate the action of a zoom lens on asecondary light source of an annular shape.

FIG. 4 is a perspective view schematically showing an internalconfiguration of a polarization monitor in FIG. 1.

FIG. 5 is an illustration schematically showing a configuration of apolarization-modulating element in FIG. 1.

FIG. 6 is an illustration to illustrate the optical activity ofcrystalline quartz.

FIG. 7 is an illustration schematically showing a secondary light sourceof an annular shape set in a azimuthal polarization state by the actionof the polarization-modulating element.

FIG. 8 is an illustration schematically showing a secondary light sourceof an annular shape set in a radially polarized state by the action ofthe polarization-modulating element.

FIG. 9 is an illustration showing a modification example in which aplurality of polarization-modulating elements are arranged in areplaceable state.

FIG. 10 is an illustration showing plural types ofpolarization-modulating elements 10 a-10 c mounted on a turret 10T as areplacing mechanism in FIG. 9.

FIGS. 11A, 11B, 11C, 11D and 11E are illustrations showing respectiveconfigurations of plural types of polarization-modulating elements 10a-10 e, respectively.

FIGS. 12A, 12B and 12C are illustrations schematically showing examplesof the secondary light source set in the azimuthal polarization state bythe action of the polarization-modulating element, respectively.

FIG. 13 is an illustration schematically showing a configuration ofpolarization-modulating element 10 f arranged rotatable around theoptical axis AX.

FIGS. 14A, 14B and 14C are illustrations schematically showing examplesof the secondary light source set in the azimuthal polarization state bythe action of polarization-modulating element 10 f, respectively.

FIGS. 15A, 15B and 15C are illustrations schematically showing examplesof the secondary light source obtained when the polarization-modulatingelement composed of elementary elements of a sector shape is arrangedrotatable around the optical axis AX, respectively.

FIG. 16 is an illustration showing an example in which thepolarization-modulating element is located at a position immediatelybefore conical axicon system 8 (or at a position near the entranceside), among locations near the pupil of the illumination opticalapparatus.

FIG. 17 is an illustration for explaining Conditions (1) and (2) to besatisfied in the modification example shown in FIG. 16.

FIG. 18 is an illustration showing an example in which thepolarization-modulating element is located near the pupil position ofimaging optical system 15, among locations near the pupil of theillumination optical apparatus.

FIG. 19 is an illustration showing a schematic configuration of wafersurface polarization monitor 90 for detecting a polarization state andlight intensity of light illuminating a wafer W.

FIG. 20 is an illustration showing a secondary light source 31 of anannular shape obtained when a quartered polarization-modulating element10 f is used to implement quartered, circumferentially polarized annularillumination.

FIG. 21 is a flowchart of a procedure of producing semiconductor devicesas microdevices.

FIG. 22 is a flowchart of a procedure of producing a liquid crystaldisplay element as a microdevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described based on theaccompanying drawings.

FIG. 1 is an illustration schematically showing a configuration of anexposure apparatus according to an embodiment of the present invention.In FIG. 1, the Z-axis is defined along a direction of a normal to awafer W being a photosensitive substrate, the Y-axis along a directionparallel to the plane of FIG. 1 in the plane of the wafer W, and theX-axis along a direction of a normal to the plane of FIG. 1 in the planeof wafer W. With reference to FIG. 1, the exposure apparatus of thepresent embodiment is provided with a light source 1 for supplyingexposure radiation (light) [(illumination light)].

The light source 1 can be, for example, a KrF excimer laser light sourcefor supplying light with the wavelength of 248 nm, an ArF excimer laserlight source for supplying light with the wavelength of 193 nm, or thelike. A nearly parallel beam emitted along the Z-direction from thelight source 1 has a cross section of a rectangular shape elongatedalong the X-direction, and is incident to a beam expander 2 consistingof a pair of lenses 2 a and 2 b. The lenses 2 a and 2 b have a negativerefracting power and a positive refracting power, respectively, in theplane of FIG. 1 (or in the YZ plane). Therefore, the beam incident tothe beam expander 2 is enlarged in the plane of FIG. 1 and shaped into abeam having a cross section of a predetermined rectangular shape.

The nearly parallel beam passing through the beam expander 2 as a beamshaping optical system is deflected into the Y-direction by a bendingmirror 3, and then travels through a quarter wave plate 4 a, a half waveplate 4 b, a depolarizer (depolarizing element) 4 c, and a diffractiveoptical element 5 for annular illumination to enter an afocal lens 6.Here the quarter wave plate 4 a, half wave plate 4 b, and depolarizer 4c constitute a polarization state converter 4, as described later. Theafocal lens 6 is an afocal system (afocal optic) set so that the frontfocal position thereof approximately coincides with the position of thediffractive optical element 5 and so that the rear focal positionthereof approximately coincides with the position of a predeterminedplane 7 indicated by a dashed line in the drawing.

In general, a diffractive optical element is constructed by forminglevel differences with the pitch of approximately the wavelength ofexposure light (illumination light) in a substrate and has the action ofdiffracting an incident beam at desired angles. Specifically, thediffractive optical element 5 for annular illumination has the followingfunction: when a parallel beam having a rectangular cross section isincident thereto, it forms a light intensity distribution of an annularshape in its far field (or Fraunhofer diffraction region).

Therefore, the nearly parallel beam incident to the diffractive opticalelement 5 as a beam transforming element forms a light intensitydistribution of an annular shape on the pupil plane of the afocal lens 6and then emerges as a nearly parallel beam from the afocal lens 6. In anoptical path between front lens unit 6 a and rear lens unit 6 b of theafocal lens 6 there is a conical axicon system 8 arranged on or near thepupil plane thereof, and the detailed configuration and action thereofwill be described later. For easier description, the fundamentalconfiguration and action will be described below, in disregard of theaction of the conical axicon system 8.

The beam through the afocal lens 6 travels through a zoom lens 9 forvariation of σ-value and a polarization-modulating element 10 and thenenters a micro fly's eye lens (or fly's eye lens) 11 as an opticalintegrator. The configuration and action of the polarization-modulatingelement 10 will be described later. The micro fly's eye lens 11 is anoptical element consisting of a number of micro lenses with a positiverefracting power arranged lengthwise and breadthwise and densely. Ingeneral, a micro fly's eye lens is constructed, for example, by forminga micro lens group by etching of a plane-parallel plate.

Here each micro lens forming the micro fly's eye lens is much smallerthan each lens element forming a fly's eye lens. The micro fly's eyelens is different from the fly's eye lens consisting of lens elementsspaced from each other, in that a number of micro lenses (microrefracting surfaces) are integrally formed without being separated fromeach other. In the sense that lens elements with a positive refractingpower are arranged lengthwise and breadthwise, however, the micro fly'seye lens is a wavefront splitting optical integrator of the same type asthe fly's eye lens. Detailed explanation concerning the micro fly's eyelens capable of being used in the present invention is disclosed, forexample, in U.S. Pat. No. 6,913,373(B2) which is incorporated herein byreference in its entirety.

The position of the predetermined plane 7 is arranged near the frontfocal position of the zoom lens 9, and the entrance surface of the microfly's eye lens 11 is arranged near the rear focal position of the zoomlens 9. In other words, the zoom lens 9 arranges the predetermined plane7 and the entrance surface of the micro fly's eye lens 11 substantiallyin the relation of Fourier transform and eventually arranges the pupilplane of the afocal lens 6 and the entrance surface of the micro fly'seye lens 11 approximately optically conjugate with each other.

Accordingly, for example, an illumination field of an annular shapecentered around the optical axis AX is formed on the entrance surface ofthe micro fly's eye lens 11, as on the pupil plane of the afocal lens 6.The entire shape of this annular illumination field similarly variesdepending upon the focal length of the zoom lens 9. Each micro lensforming the micro fly's eye lens 11 has a rectangular cross sectionsimilar to a shape of an illumination field to be formed on a mask M(eventually, a shape of an exposure region to be formed on a wafer W).

The beam incident to the micro fly's eye lens 11 is two-dimensionallysplit by a number of micro lenses to form on or near the rear focalplane (eventually on the illumination pupil) a secondary light sourcehaving much the same light intensity distribution as the illuminationfield fanned by the incident beam, i.e., a secondary light sourceconsisting of a substantial surface illuminant of an annular shapecentered around the optical axis AX. Beams from the secondary lightsource formed on or near the rear focal plane of the micro fly's eyelens 11 travel through beam splitter 12 a and condenser optical system13 to superposedly illuminate a mask blind 14.

In this manner, an illumination field of a rectangular shape accordingto the shape and focal length of each micro lens forming the micro fly'seye lens 11 is formed on the mask blind 14 as an illumination fieldstop. The internal configuration and action of polarization monitor 12incorporating a beam splitter 12 a will be described later. Beamsthrough a rectangular aperture (light transmitting portion) of the maskblind 14 are subject to light condensing action of imaging opticalsystem 15 and thereafter superposedly illuminate the mask M on which apredetermined pattern is formed.

Namely, the imaging optical system 15 forms an image of the rectangularaperture of the mask blind 14 on the mask M. A beam passing through thepattern of mask M travels through a projection optical system PL to forman image of the mask pattern on the wafer W being a photosensitivesubstrate. In this manner, the pattern of the mask M is sequentiallyprinted in each exposure area on the wafer W through full-wafer exposureor scan exposure with two-dimensional drive control of the wafer W inthe plane (XY plane) perpendicular to the optical axis AX of theprojection optical system PL.

In the polarization state converter 4, the quarter wave plate 4 a isarranged so that its crystallographic axis is rotatable around theoptical axis AX, and it transforms incident light of ellipticalpolarization into light of linear polarization. The half wave plate 4 bis arranged so that its crystallographic axis is rotatable around theoptical axis AX, and it changes the plane of polarization of linearlypolarized light incident thereto. The depolarizer 4 c is composed of awedge-shaped crystalline quartz prism and a wedge-shaped fused silicaprism having complementary shapes. The crystalline quartz prism and thefused silica prism are constructed as an integral prism assembly so asto be set into and away from the illumination optical path.

Where the light source 1 is the KrF excimer laser light source or theArF excimer laser light source, light emitted from these light sourcestypically has the degree of polarization of 95% or more and light ofalmost linear polarization is incident to the quarter wave plate 4 a.However, if a right-angle prism as a back-surface reflector isinterposed in the optical path between the light source 1 and thepolarization state converter 4, the linearly polarized light will bechanged into elliptically polarized light by virtue of total reflectionin the right-angle prism unless the plane of polarization of theincident, linearly polarized light agrees with the P-polarization planeor S-polarization plane.

In the case of the polarization state converter 4, for example, even iflight of elliptical polarization is incident thereto because of thetotal reflection in the right-angle prism, light of linear polarizationtransformed by the action of the quarter wave plate 4 a will be incidentto the half wave plate 4 b. Where the crystallographic axis of the halfwave plate 4 b is set at an angle of 0° or 90° relative to the plane ofpolarization of the incident, linearly polarized light, the light oflinear polarization incident to the half wave plate 4 b will pass as itis, without change in the plane of polarization.

Where the crystallographic axis of the half wave plate 4 b is set at anangle of 45° relative to the plane of polarization of the incident,linearly polarized light, the light of linear polarization incident tothe half wave plate 4 b will be transformed into light of linearpolarization with change of polarization plane of 90°. Furthermore,where the crystallographic axis of the crystalline quartz prism in thedepolarizer 4 c is set at an angle of 45° relative to the polarizationplane of the incident, linearly polarized light, the light of linearpolarization incident to the crystalline quartz prism will betransformed (or depolarized) into light in an unpolarized state.

The polarization state converter 4 is arranged as follows: when thedepolarizer 4 c is positioned in the illumination optical path, thecrystallographic axis of the crystalline quartz prism makes the angle of45° relative to the polarization plane of the incident, linearlypolarized light. Incidentally, where the crystallographic axis of thecrystalline quartz prism is set at the angle of 0° or 90° relative tothe polarization plane of the incident, linearly polarized light, thelight of linear polarization incident to the crystalline quartz prismwill pass as it is, without change of the polarization plane. Where thecrystallographic axis of the half wave plate 4 b is set at an angle of22.5° relative to the polarization plane of incident, linearly polarizedlight, the light of linear polarization incident to the half wave plate4 b will be transformed into light in an unpolarized state including alinear polarization component directly passing without change of thepolarization plane and a linear polarization component with thepolarization plane rotated by 90°.

The polarization state converter 4 is arranged so that light of linearpolarization is incident to the half wave plate 4 b, as described above,and, for easier description hereinafter, it is assumed that light oflinear polarization having the direction of polarization (direction ofthe electric field) along the Z-axis in FIG. 1 (hereinafter referred toas “Z-directionally polarized light”) is incident to the half wave plate4 b. When the depolarizer 4 c is positioned in the illumination opticalpath and when the crystallographic axis of the half wave plate 4 b isset at the angle of 0° or 90° relative to the polarization plane(direction of polarization) of the Z-directionally polarized lightincident thereto, the light of Z-directional polarization incident tothe half wave plate 4 b passes as kept as Z-directionally polarizedlight without change of the polarization plane and enters thecrystalline quartz prism in the depolarizer 4 c. Since thecrystallographic axis of the crystalline quartz prism is set at theangle of 45° relative to the polarization plane of the Z-directionallypolarized light incident thereto, the light of Z-directionalpolarization incident to the crystalline quartz prism is transformedinto light in an unpolarized state.

The light depolarized through the crystalline quartz prism travelsthrough the quartz prism as a compensator for compensating the travelingdirection of the light and is incident into the diffractive opticalelement 5 while being in the depolarized state. On the other hand, ifthe crystallographic axis of the half wave plate 4 b is set at the angleof 45° relative to the polarization plane of the Z-directionallypolarized light incident thereto, the light of Z-directionalpolarization incident to the half wave plate 4 b will be rotated in thepolarization plane by 90° and transformed into light of linearpolarization having the polarization direction (direction of theelectric field) along the X-direction in FIG. 1 (hereinafter referred toas “X-directionally polarized light”) and the X-directionally polarizedlight will be incident to the crystalline quartz prism in thedepolarizer 4 c. Since the crystallographic axis of the crystallinequartz prism is set at the angle of 45° relative to the polarizationplane of the incident, X-directionally polarized light as well, thelight of X-directional polarization incident to the crystalline quartzprism is transformed into light in the depolarized state, and the lighttravels through the quartz prism to be incident in the depolarized stateinto the diffractive optical element 5.

In contrast, when the depolarizer 4 c is set away from the illuminationoptical path, if the crystallographic axis of the half wave plate 4 b isset at the angle of 0° or 90° relative to the polarization plane of theZ-directionally polarized light incident thereto, the light ofZ-directional polarization incident to the half wave plate 4 b will passas kept as Z-directionally polarized light without change of thepolarization plane, and will be incident in the Z-directionallypolarized state into the diffractive optical element 5. If thecrystallographic axis of the half wave plate 4 b is set at the angle of45° relative to the polarization plane of the Z-directionally polarizedlight incident thereto on the other hand, the light of Z-directionalpolarization incident to the half wave plate 4 b will be transformedinto light of X-directional polarization with the polarization planerotated by 90°, and will be incident in the X-directionally polarizedstate into the diffractive optical element 5.

In the polarization state converter 4, as described above, the light inthe depolarized state can be made incident to the diffractive opticalelement 5 when the depolarizer 4 c is set and positioned in theillumination optical path. When the depolarizer 4 c is set away from theillumination optical path and when the crystallographic axis of the halfwave plate 4 b is set at the angle of 0° or 90° relative to thepolarization plane of the Z-directionally polarized light incidentthereto, the light in the Z-directionally polarized state can be madeincident to the diffractive optical element 5. Furthermore, when thedepolarizer 4 c is set away from the illumination optical path and whenthe crystallographic axis of the half wave plate 4 b is set at the angleof 45° relative to the polarization plane of the Z-directionallypolarized light incident thereto, the light in the X-directionallypolarized state can be made incident to the diffractive optical element5.

In other words, the polarization state converter 4 is able to switch thepolarization state of the incident light into the diffractive opticalelement 5 (therefore, the polarization state of light to illuminate themask M and wafer W) between the linearly polarized state and theunpolarized state through the action of the polarization state converterconsisting of the quarter wave plate 4 a, half wave plate 4 b, anddepolarizer 4 c, and, in the case of the linearly polarized state, it isable to switch between mutually orthogonal polarization states (betweenthe Z-directional polarization and the X-directional polarization).

Furthermore, when the polarization state converter 4 is so set that thehalf wave plate 4 b and depolarizer 4 c both are set away from theillumination optical path and that the crystallographic axis of thequarter wave plate 4 a makes a predetermined angle relative to theincident, elliptically polarized light, light in a circularly polarizedstate can be made incident to the diffractive optical element 5. Ingeneral, the polarization state of incident light to the diffractiveoptical element 5 can also be set in a linearly polarized state having adirection of polarization along an arbitrary direction by the action ofthe half wave plate 4 b.

Next, the conical axicon system 8 is composed of a first prism member 8a whose plane is kept toward the light source and whose refractingsurface of a concave conical shape is kept toward the mask, and a secondprism member 8 b whose plane is kept toward the mask and whoserefracting surface of a convex conical shape is kept toward the lightsource, in order from the light source side. The refracting surface ofthe concave conical shape of the first prism member 8 a and therefracting surface of the convex conical shape of the second prismmember 8 b are formed in a complementary manner so as to be able to bebrought into contact with each other. At least one of the first prismmember 8 a and the second prism member 8 b is arranged movable along theoptical axis AX, so that the spacing can be varied between therefracting surface of the concave conical shape of the first prismmember 8 a and the refracting surface of the convex conical shape of thesecond prism member 8 b.

In a state in which the refracting surface of the concave conical shapeof the first prism member 8 a and the refracting surface of the convexconical shape of the second prism member 8 b are in contact with eachother, the conical axicon system 8 functions as a plane-parallel plateand has no effect on the secondary light source of the annular shapeformed. However, when the refracting surface of the concave conicalshape of the first prism member 8 a and the refracting surface of theconvex conical shape of the second prism member 8 b are spaced from eachother, the conical axicon system 8 functions a so-called beam expander.Therefore, the angle of the incident beam to the predetermined plane 7varies according to change in the spacing of the conical axicon system8.

FIG. 2 is an illustration to illustrate the action of the conical axiconsystem on the secondary light source of the annular shape. Withreference to FIG. 2, the secondary light source 30 a of the minimumannular shape formed in a state where the spacing of the conical axiconsystem 8 is zero and where the focal length of the zoom lens 9 is set atthe minimum (this state will be referred to hereinafter as a “standardstate”) is changed into secondary light source 30 b of an annular shapewith the outside diameter and inside diameter both enlarged and withoutchange in the width (half of the difference between the inside diameterand the outside diameter: indicated by arrows in the drawing) when thespacing of the conical axicon system 8 is increased from zero to apredetermined value. In other words, an annular ratio (insidediameter/outside diameter) and size (outside diameter) both vary throughthe action of the conical axicon system 8, without change in the widthof the secondary light source of the annular shape.

FIG. 3 is an illustration to illustrate the action of the zoom lens onthe secondary light source of the annular shape. With reference to FIG.3, the secondary light source 30 a of the annular shape formed in thestandard state is changed into secondary light source 30 c of an annularshape whose entire shape is similarly enlarged by increasing the focallength of the zoom lens 9 from the minimum to a predetermined value. Inother words, the width and size (outside diameter) both vary through theaction of zoom lens 9, without change in the annular ratio of thesecondary light source of the annular shape.

FIG. 4 is a perspective view schematically showing the internalconfiguration of the polarization monitor shown in FIG. 1. Withreference to FIG. 4, the polarization monitor 12 is provided with afirst beam splitter 12 a disposed in the optical path between the microfly's eye lens 11 and the condenser optical system 13. The first beamsplitter 12 a has, for example, the form of a non-coated plane-parallelplate made of quartz glass (i.e., raw glass), and has a function oftaking reflected light in a polarization state different from apolarization state of incident light, out of the optical path.

The light taken out of the optical path by the first beam splitter 12 ais incident to a second beam splitter 12 b. The second beam splitter 12b has, for example, the form of a non-coated plane-parallel plate madeof quartz glass as the first beam splitter 12 a does, and has a functionof generating reflected light in a polarization state different from thepolarization state of incident light. The polarization monitor is so setthat the P-polarized light for the first beam splitter 12 a becomes theS-polarized light for the second beam splitter 12 b and that theS-polarized light for the first beam splitter 12 a becomes theP-polarized light for the second beam splitter 12 b.

Light transmitted by the second beam splitter 12 b is detected by firstlight intensity detector 12 c, while light reflected by the second beamsplitter 12 b is detected by second light intensity detector 12 d.Outputs from the first light intensity detector 12 c and from the secondlight intensity detector 12 d are supplied each to a controller (notshown). The controller drives the quarter wave plate 4 a, half waveplate 4 b, and depolarizer 4 c constituting the polarization stateconverter 4, according to need.

As described above, the reflectance for the P-polarized light and thereflectance for the S-polarized light are substantially different in thefirst beam splitter 12 a and in the second beam splitter 12 b. In thepolarization monitor 12, therefore, the reflected light from the firstbeam splitter 12 a includes the S-polarization component (i.e., theS-polarization component for the first beam splitter 12 a andP-polarization component for the second beam splitter 12 b), forexample, which is approximately 10% of the incident light to the firstbeam splitter 12 a, and the P-polarization component (i.e., theP-polarization component for the first beam splitter 12 a andS-polarization component for the second beam splitter 12 b), forexample, which is approximately 1% of the incident light to the firstbeam splitter 12 a.

The reflected light from the second beam splitter 12 b includes theP-polarization component (i.e., the P-polarization component for thefirst beam splitter 12 a and S-polarization component for the secondbeam splitter 12 b), for example, which is approximately 10%×1%=0.1% ofthe incident light to the first beam splitter 12 a, and theS-polarization component (i.e., the S-polarization component for thefirst beam splitter 12 a and P-polarization component for the secondbeam splitter 12 b), for example, which is approximately 1%×10%=0.1% ofthe incident light to the first beam splitter 12 a.

In the polarization monitor 12, as described above, the first beamsplitter 12 a has the function of extracting the reflected light in thepolarization state different from the polarization state of the incidentlight out of the optical path in accordance with its reflectioncharacteristic. As a result, though there is slight influence ofvariation of polarization due to the polarization characteristic of thesecond beam splitter 12 b, it is feasible to detect the polarizationstate (degree of polarization) of the incident light to the first beamsplitter 12 a and, therefore, the polarization state of the illuminationlight to the mask M, based on the output from the first light intensitydetector 12 c (information about the intensity of transmitted light fromthe second beam splitter 12 b, i.e., information about the intensity oflight virtually in the same polarization state as that of the reflectedlight from the first beam splitter 12 a).

The polarization monitor 12 is so set that the P-polarized light for thefirst beam splitter 12 a becomes the S-polarized light for the secondbeam splitter 12 b and that the S-polarized light for the first beamsplitter 12 a becomes the P-polarized light for the second beam splitter12 b. As a result, it is feasible to detect the light quantity(intensity) of the incident light to the first beam splitter 12 a and,therefore, the light quantity of the illumination light to the mask M,with no substantial effect of the change in the polarization state ofthe incident light to the first beam splitter 12 a, based on the outputfrom the second light intensity detector 12 d (information about theintensity of light successively reflected by the first beam splitter 12a and the second beam splitter 12 b).

In this manner, it is feasible to detect the polarization state of theincident light to the first beam splitter 12 a and, therefore, todetermine whether the illumination light to the mask M is in the desiredunpolarized state, linearly polarized state, or circularly polarizedstate, using the polarization monitor 12. When the controller determinesthat the illumination light to the mask M (eventually, to the wafer W)is not in the desired unpolarized state, linearly polarized state, orcircularly polarized state, based on the detection result of thepolarization monitor 12, it drives and adjusts the quarter wave plate 4a, half wave plate 4 b, and depolarizer 4 c constituting thepolarization state converter 4 so that the state of the illuminationlight to the mask M can be adjusted into the desired unpolarized state,linearly polarized state, or circularly polarized state.

Quadrupole illumination can be implemented by setting a diffractiveoptical element for quadrupole illumination (not shown) in theillumination optical path, instead of the diffractive optical element 5for annular illumination. The diffractive optical element for quadrupoleillumination has such a function that when a parallel beam having arectangular cross section is incident thereto, it forms a lightintensity distribution of a quadrupole shape in the far field thereof.Therefore, the beam passing through the diffractive optical element forquadrupole illumination forms an illumination field of a quadrupoleshape consisting of four circular illumination fields centered aroundthe optical axis AX, for example, on the entrance surface of the microfly's eye lens 11. As a result, the secondary light source of the samequadrupole shape as the illumination field formed on the entrancesurface is also formed on or near the rear focal plane of the microfly's eye lens 11.

In addition, ordinary circular illumination can be implemented bysetting a diffractive optical element for circular illumination (notshown) in the illumination optical path, instead of the diffractiveoptical element 5 for annular illumination. The diffractive opticalelement for circular illumination has such a function that when aparallel beam having a rectangular cross section is incident thereto, itforms a light intensity distribution of a circular shape in the farfield. Therefore, a beam passing through the diffractive optical elementfor circular illumination forms a circular illumination field centeredaround the optical axis AX, for example, on the entrance surface of themicro fly's eye lens 11. As a result, the secondary light source of thesame circular shape as the illumination field formed on the entrancesurface is also formed on or near the rear focal plane of the microfly's eye lens 11.

Furthermore, a variety of multipole illuminations (dipole illumination,octapole illumination, etc.) can be implemented by setting otherdiffractive optical elements for multipole illuminations (not shown),instead of the diffractive optical element 5 for annular illumination.Likewise, modified illuminations in various forms can be implemented bysetting diffractive optical elements with appropriate characteristics(not shown) in the illumination optical path, instead of the diffractiveoptical element 5 for annular illumination.

FIG. 5 is an illustration schematically showing the configuration of thepolarization-modulating element shown in FIG. 1. FIG. 6 is anillustration to illustrate the optical activity of crystalline quartz.FIG. 7 is an illustration schematically showing the secondary lightsource of the annular shape set in the azimuthal polarization state bythe action of the polarization-modulating element. Thepolarization-modulating element 10 according to the present embodimentis located immediately before the micro fly's eye lens 11, i.e., on ornear the pupil of the illumination optical apparatus (1 to PL).Therefore, in the case of the annular illumination, the beam having anapproximately annular cross section centered around the optical axis AXis incident to the polarization-modulating element 10.

With reference to FIG. 5, the polarization-modulating element 10 has aneffective region of an annular shape centered around the optical axis AXas a whole, and this effective region of the annular shape is composedof eight elementary elements of a sector shape as circumferentiallyequally divided around the optical axis AX. Among these eight elementaryelements, a pair of elementary elements facing each other with theoptical axis AX in between have the same characteristic. Namely, theeight elementary elements include four types of elementary elements10A-10D two each with different thicknesses (lengths in the direction ofthe optical axis) along the direction of transmission of light(Y-direction).

Specifically, the thickness of the first elementary elements 10A is thelargest, the thickness of the fourth elementary elements 10D is thesmallest, and the thickness of the second elementary elements 10B is setlarger than the thickness of the third elementary elements 10C. As aresult, one surface (e.g., the entrance surface) of thepolarization-modulating element 10 is planar, while the other surface(e.g., the exit surface) is uneven because of the differences among thethicknesses of the elementary elements 10A-10D. It is also possible toform the both surfaces (the entrance surface and exit surface) of thepolarization-modulating element 10 in an uneven shape.

In the present embodiment, each elementary element 10A-10D is made ofcrystalline quartz as a crystalline material being an optical materialwith optical activity, and the crystallographic axis of each elementaryelement 10A-10D is set to be approximately coincident with the opticalaxis AX, i.e., with the traveling direction of incident light. Theoptical activity of crystalline quartz will be briefly described belowwith reference to FIG. 6. With reference to FIG. 6, an optical member100 of a plane-parallel plate shape made of crystalline quartz and in athickness d is arranged so that its crystallographic axis coincides withthe optical axis AX. In this case, by virtue of the optical activity ofthe optical member 100, linearly polarized light incident theretoemerges in a state in which its-polarization direction is rotated by θaround the optical axis AX.

At this time, the rotation angle (angle of optical rotation) θ of thepolarization direction due to the optical activity of the optical member100 is represented by Eq (a) below, using the thickness d of the opticalmember 100 and the rotatory power ρ of crystalline quartz.θ=d·ρ  (a)

In general, the rotatory power ρ of crystalline quartz has wavelengthdependence (a property that the value of the optical rotatory powerdiffers depending upon the wavelength of light used: optical rotatorydispersion) and, specifically, it tends to increase with decrease in thewavelength of light used. According to the description on page 167 in“Applied Optics II,” the rotatory power ρ of crystalline quartz forlight having the wavelength of 250.3 nm is 153.9°/mm.

In the present embodiment, the first elementary elements 10A aredesigned in such a thickness dA that when linearly polarized lighthaving the polarization direction along the Z-direction is incidentthereto, they output light of linear polarization having thepolarization direction along a direction resulting from +180° rotationof the Z-direction around the Y-axis, i.e., along the Z-direction. Inthis case, therefore, the polarization direction of beams passingthrough a pair of arc (bow shape) regions 31A formed by beams subject tothe optical rotating action of a pair of first elementary elements 10A,in the secondary light source 31 of the annular shape shown in FIG. 7,is the Z-direction.

The second elementary elements 10B are designed in such a thickness dBthat when linearly polarized light having the polarization directionalong the Z-direction is incident thereto, they output light of linearpolarization having the polarization direction along a directionresulting from +135° rotation of the Z-direction around the Y-axis,i.e., along a direction resulting from −45° rotation of the Z-directionaround the Y-axis. In this case, therefore, the polarization directionof beams passing through a pair of arc (bow shape) regions 31B formed bybeams subject to the optical rotating action of a pair of secondelementary elements 10B, in the secondary light source 31 of the annularshape shown in FIG. 7, is a direction obtained by rotating theZ-direction by −45° around the Y-axis.

The third elementary elements 10C are designed in such a thickness dCthat when linearly polarized light having the polarization directionalong the Z-direction is incident thereto, they output light of linearpolarization having the polarization direction along a directionresulting from +90° rotation of the Z-direction around the Y-axis, i.e.,along the X-direction. In this case, therefore, the polarizationdirection of beams passing through a pair of arc (bow shape) regions 31Cformed by beams subject to the optical rotating action of a pair ofthird elementary elements 10C, in the secondary light source 31 of theannular shape shown in FIG. 7, is the X-direction.

The fourth elementary elements 10D are designed in such a thickness dDthat when linearly polarized light having the polarization directionalong the Z-direction is incident thereto, they output light of linearpolarization having the polarization direction along a directionresulting from +45° rotation of the Z-direction around the Y-axis. Inthis case, therefore, the polarization direction of beams passingthrough a pair of arc (bow shape) regions 31D formed by beams subject tothe optical rotating action of a pair of fourth elementary elements 10D,in the secondary light source 31 of the annular shape shown in FIG. 7,is a direction obtained by rotating the Z-direction by +45° around theY-axis.

The polarization-modulating element 10 can be constructed by combiningthe eight elementary elements prepared separately, or thepolarization-modulating element 10 can also be constructed by formingthe required uneven shape (level differences) in a crystalline quartzsubstrate of a plane-parallel plate shape. For allowing the ordinarycircular illumination with the polarization-modulating element 10 beingkept in the optical path, the polarization-modulating element 10 isprovided with a central region 10E of a circular shape in the size notless than 3/10, preferably, not less than ⅓ of the radial size of theeffective region of the polarization-modulating element 10 and withoutoptical activity. The central region 10E may be made of an opticalmaterial without optical activity, for example, like quartz, or may besimply a circular aperture. It is, however, noted that the centralregion 10E is not an essential element for the polarization-modulatingelement 10. The size of the central region 10E determines the boundarybetween the region in the azimuthal polarization state and the otherregion.

In the present embodiment, on the occasion of the circumferentiallypolarized annular illumination (modified illumination in which beamspassing through the secondary light source of the annular shape are setin the azimuthal polarization state), the linearly polarized lighthaving the polarization direction along the Z-direction is made incidentto the polarization-modulating element 10. As a result, as shown in FIG.7, the secondary light source of the annular shape (illumination pupildistribution of annular shape) 31 is formed on or near the rear focalplane of the micro fly's eye lens 11, and beams passing through thissecondary light source 31 of the annular shape are set in the azimuthalpolarization state. In the azimuthal polarization state, the beamspassing through the respective arc (bow shape) regions 31A-31Dconstituting the secondary light source 31 of the annular shape turninto a linearly polarized state having the polarization directionapproximately coincident with a tangential direction to a circlecentered around the optical axis AX, at the central position along thecircumferential direction of each arc region 31A-31D.

In this manner, the present embodiment, different from the conventionaltechnology giving rise to the large loss of light quantity at theaperture stop, is able to form the secondary light source 31 of theannular shape in the azimuthal polarization state, with no substantialloss of light quantity, through the optical rotating action of thepolarization-modulating element 10. In other words, the illuminationoptical apparatus of the present embodiment is able to form theillumination pupil distribution of the annular shape in the azimuthalpolarization state while well suppressing the loss of light quantity.Furthermore, since the present embodiment uses the polarizing action ofthe optical elements, it has the excellent effect that thepolarization-modulating element itself is extremely easy to produce and,typically, the thickness tolerance of each elementary element can be setto be extremely loose.

In the circumferentially polarized annular illumination based on theillumination pupil distribution of the annular shape in the azimuthalpolarization state, the light illuminating the wafer W as a last surfaceto be illuminated is in a polarized state in which the principalcomponent is S-polarized light. Here the S-polarized light is linearlypolarized light having the polarization direction along a directionnormal to the plane of incidence (i.e., polarized light with theelectric vector oscillating in the direction normal to the plane ofincidence). The plane of incidence is defined as follows: when lightarrives at a boundary surface of a medium (surface to be illuminated:surface of wafer W), the plane of incidence is a plane including anormal to the boundary surface at that point and the direction ofincidence of light.

Consequently, the circumferentially polarized annular illuminationrealizes an improvement in the optical performance (depth of focus andthe like) of the projection optical system and enables formation of amask pattern image with high contrast on the wafer (photosensitivesubstrate). Namely, since the exposure apparatus of the presentembodiment uses the illumination optical apparatus capable of formingthe illumination pupil distribution of the annular shape in theazimuthal polarization state while well suppressing the loss of lightquantity, it is able to transcribe a fine pattern under an appropriateillumination condition faithfully and with high throughput.

Incidentally, the present embodiment enables radially polarized annularillumination (modified illumination in which beams passing through thesecondary light source of the annular shape are set in a radiallypolarized state) by injecting linearly polarized light having thepolarization direction along the X-direction into thepolarization-modulating element 10 and thereby setting the beams passingthrough the secondary light source 32 of the annular shape in theradially polarized state as shown in FIG. 8. In the radially polarizedstate, beams passing through the respective arc (bow shape) regions32A-32D constituting the secondary light source 32 of the annular shapeare in the linearly polarized state having the polarization directionapproximately coincident with a radial direction of a circle centeredaround the optical axis AX, at the central position along thecircumferential direction of each arc region 32A-32D.

In the radially polarized annular illumination based on the illuminationpupil distribution of the annular shape in the radially polarized state,the light illuminating the wafer W as a last surface to be illuminatedis in a polarized state in which the principal component is P-polarizedlight. The P-polarized light herein is linearly polarized light havingthe polarization direction along a direction parallel to the plane ofincidence defined as described above (i.e., polarized light with theelectric vector oscillating in the direction parallel to the plane ofincidence). In consequence, the radially polarized annular illuminationenables formation of a good mask pattern image on the wafer(photosensitive substrate) while keeping the reflectance of light low onthe resist applied onto the wafer W.

The above-described embodiment realizes the circumferentially polarizedannular illumination and the radially polarized annular illumination byswitching the beam incident to the polarization-modulating element 10between the linearly polarized state having the polarization directionalong the Z-direction and the linearly polarized state having thepolarization direction along the X-direction. However, without having tobe limited to this, it is also possible to realize the circumferentiallypolarized annular illumination and the radially polarized annularillumination, for example, by switching the polarization-modulatingelement 10 between a first state shown in FIG. 5 and a second stateresulting from 90° rotation around the optical axis AX, for the incidentbeam in the linearly polarized state having the polarization directionalong the Z-direction or along the X-direction.

In the foregoing embodiment the polarization-modulating element 10 islocated immediately before the micro fly's eye lens 11. However, withouthaving to be limited to this, the polarization-modulating element 10 canalso be located generally on or near the pupil of the illuminationoptical apparatus (1 to PL), e.g., on or near the pupil of theprojection optical system PL, on or near the pupil of the imagingoptical system 15, or immediately before the conical axicon system 8 (onor near the pupil of afocal lens 6).

However, where the polarization-modulating element 10 is located in theprojection optical system PL or in the imaging optical system 15, therequired effective diameter (clear aperture diameter) of thepolarization-modulating element 10 is prone to become large, and it israther undesirable in view of the current circumstances in which it isdifficult to obtain a large crystalline quartz substrate with highquality. When the polarization-modulating element 10 is locatedimmediately before the conical axicon system 8, the required effectivediameter (clear aperture diameter) of the polarization-modulatingelement 10 can be kept small. However, the distance is long to the waferW being the last surface to be illuminated, and an element to change thepolarization state like an antireflection coat on a lens or a reflectingfilm on a mirror is likely to be interposed in the optical path to thewafer. Therefore, this arrangement is not so preferable. In passing, theantireflection coat on the lens or the reflecting film on the mirror islikely to cause the difference of reflectance depending upon thepolarization states (P-polarization and S-polarization) and angles ofincidence and, in turn, to change the polarization state of light.

In the foregoing embodiment, at least one surface of thepolarization-modulating element 10 (e.g., the exit surface) is formed inthe uneven shape and, therefore, the polarization-modulating element 10has a thickness profile discretely (discontinuously) varying in thecircumferential direction. However, without having to be limited tothis, at least one surface of the polarization-modulating element 10(e.g., the exit surface) can also be formed in such a curved shape thatthe polarization-modulating element 10 has a thickness profile virtuallydiscontinuously varying in the circumferential direction.

In the foregoing embodiment the polarization-modulating element 10 iscomposed of the eight elementary elements of the sector shapecorresponding to the division of the effective region of the annularshape into eight segments. However, without having to be limited tothis, the polarization-modulating element 10 can also be composed, forexample, of eight elementary elements of a sector shape corresponding todivision of the effective region of a circular shape into eightsegments, or of four elementary elements of a sector shape correspondingto division of the effective region of a circular shape or annular shapeinto four segments, or of sixteen elementary elements of a sector shapecorresponding to division of the effective region of a circular shape orannular shape into sixteen segments. Namely, a variety of modificationexamples can be contemplated as to the shape of the effective region ofthe polarization-modulating element 10, the number of segments in thedivision of the effective region (the number of elementary elements),and so on.

In the foregoing embodiment each elementary element 10A-10D (therefore,the polarization-modulating element 10) is made of crystalline quartz.However, without having to be limited to this, each elementary elementcan also be made of another appropriate optical material with opticalactivity. In this case, it is preferable to use an optical material withan optical rotatory power of not less than 100°/mm for light of awavelength used. Namely, use of an optical material with a small opticalrotatory power is undesirable because the thickness necessary forobtaining the required rotation angle of the polarization directionbecomes too large, so as to cause a loss of light quantity.

In the foregoing embodiment the polarization-modulating element 10 isfixedly provided in the illumination optical path, but thepolarization-modulating element 10 may be arranged to be set into andaway from the illumination optical path. The above embodiment showed theexample as a combination of the annular illumination with theS-polarized light for the wafer W, but it is also possible to combinethe S-polarized light for the wafer W with multipole illumination, suchas dipole or quadrupole illumination, and with circular illumination. Inthe foregoing embodiment the illumination conditions for the mask M andthe imaging conditions (numerical aperture, aberrations, etc.) for thewafer W can be automatically set, for example, according to the type ofthe pattern on the mask M or the like.

FIG. 9 shows a modification example in which a plurality ofpolarization-modulating elements are arranged in a replaceable state.The modification example of FIG. 9 has a configuration similar to theembodiment shown in FIG. 1, but it is different in that it has a turret10T enabling replacement of the plurality of polarization-modulatingelements.

FIG. 10 is an illustration showing plural types ofpolarization-modulating elements 10 a-10 e mounted on the turret 10T asa replacing mechanism in FIG. 9. In this modification example, as shownin FIGS. 9 and 10, the plural types of polarization-modulating elements10 a-10 e are provided on the turret 10T rotatable around an axis alonga direction parallel to the optical axis AX, and these plural types ofpolarization-modulating elements 10 a-10 e are arranged replaceable byrotation operation of the turret 10T. FIG. 9 depicts only thepolarization-modulating elements 10 a, 10 b out of the plural types ofpolarization-modulating elements 10 a-10 e. The replacing mechanism forthe polarization-modulating elements is not limited to the turret 10T,but may be, for example, a slider.

FIGS. 11A-11E are illustrations showing respective configurations of theplural types of polarization-modulating elements 10 a-10 e. In FIG. 11A,the first polarization-modulating element 10 a has the sameconfiguration as the polarization-modulating element 10 of theembodiment shown in FIG. 5. In FIG. 11B, the secondpolarization-modulating element 10 b has a configuration similar to thepolarization-modulating element 10 a shown in FIG. 11A, but is differentin that it is provided with a depolarizing member 104 c in centralregion 10E. This depolarizing member 104 c has a configuration similarto the depolarizer 4 c shown in FIG. 1, and has a function oftransforming incident light of linear polarization into light in adepolarized state.

In FIG. 11C, the third polarization-modulating element 10 c has aconfiguration similar to the polarization-modulating element 10 a shownin FIG. 11A, but is different in that the size of the central region 10Eis larger (i.e., in that the width of the first to fourth elementaryelements 10A-10D is smaller). In FIG. 11D, the fourthpolarization-modulating element 10 d has a configuration similar to thepolarization-modulating element 10 c shown in FIG. 11C, but is differentin that a depolarizing member 104 c is provided in the central region10E.

In FIG. 11E, the fifth polarization-modulating element 10 e isconstructed by combining six elementary elements 10C, 10F, 10G,different from the eight elementary elements. The fifthpolarization-modulating element 10 e has the effective region of anannular shape centered around the optical axis AX as a whole, and thiseffective region of the annular shape is composed of six elementaryelements 10C, 10F, 10G of a sector shape as equally divided in thecircumferential direction around the optical axis AX. Among these sixelementary elements 10C, 10F, 10G, a pair of elementary elements facingeach other with the optical axis AX in between have the samecharacteristic. Namely, the six elementary elements 10C, 10F, 10Ginclude three types of elementary elements 10C, 10F, 10G with mutuallydifferent thicknesses (lengths in the direction of the optical axis)along the direction of transmission of light (the Y-direction) two each.

The elementary elements 10C are members having the same function as thethird elementary elements 10C shown in FIG. 7, and thus the descriptionof the function thereof is omitted herein. The elementary elements 10Fare designed in such a thickness dF that when linearly polarized lighthaving the polarization direction along the Z-direction is incidentthereto, they output light of linear polarization having thepolarization direction along a direction resulting from +150° rotationof the Z-direction around the Y-axis, i.e., along a direction resultingfrom −30° rotation of the Z-direction around the Y-axis. The elementaryelements 10G are designed in such a thickness dG that when linearlypolarized light having the polarization direction along the Z-directionis incident thereto, they output light of linear polarization having thepolarization direction along a direction resulting from +30° rotation ofthe Z-direction around the Y-axis. A depolarizing member 104 c may beprovided in place of the central region 10E.

Referring again to FIG. 10, the turret 10T is provided with an opening40 without any polarization-modulating element, and this opening 40 islocated in the illumination optical path in a case where anotherpolarized illumination is implemented different from thecircumferentially polarized illumination, or in a case where unpolarizedillumination is implemented under a large σ-value (σ value=numericalaperture on the mask side of the illumination opticalapparatus/numerical aperture on the mask side of the projection opticalsystem).

The above described only the examples wherein the central region 10Emade of the circular opening or the material without optical activity,or the depolarizing member 104 c was provided in the central region ofthe polarization-modulating elements 10 a-10 e mounted on the turret10T, but it is also possible to mount polarization-modulating elementswithout central region 10E nor depolarizing member 104 c (i.e.,polarization-modulating elements consisting of elementary elements of asector shape).

FIGS. 12A-12C are illustrations schematically showing examples of thesecondary light source set in the azimuthal polarization state by theaction of the polarization-modulating element. In FIGS. 12A-12C, thepolarization-modulating element is also illustrated in a superimposedmanner in order to facilitate understanding.

FIG. 12A shows the secondary light source 33 of an octapole shape in acase where a diffractive optical element (beam transforming element) forforming a light intensity distribution of an octapole shape in the farfield (or Fraunhofer diffraction region) is located in the illuminationoptical path, instead of the diffractive optical element 5, and wherethe polarization-modulating element 10 a or 10 b is located in theillumination optical path. Beams passing through the secondary lightsource 33 of the octapole shape are set in the azimuthal polarizationstate. In the azimuthal polarization state, the beams passing throughthe respective eight circular regions 33A-33D constituting the secondarylight source 33 of the octapole shape are in the linearly polarizedstate having the polarization direction approximately coincident with acircumferential direction of a circle connecting these eight circularregions 33A-33D, i.e., with a tangential direction to the circleconnecting these eight circular regions 33A-33D. FIG. 12A shows theexample wherein the secondary light source 33 of the octapole shape iscomposed of the eight circular regions 33A-33D, but the shape of theeight regions is not limited to the circular shape.

FIG. 12B shows the secondary light source 34 of a quadrupole shape in acase where a diffractive optical element (beam transforming element) forforming a light intensity distribution of a quadrupole shape in the farfield (or Fraunhofer diffraction region) is located in the illuminationoptical path, instead of the diffractive optical element 5, and wherethe polarization-modulating element 10 c or 10 d is located in theillumination optical path. Beams passing through the secondary lightsource 34 of the quadrupole shape are set in the azimuthal polarizationstate. In the azimuthal polarization state, the beams passing throughthe respective four regions 34A, 34C constituting the secondary lightsource 34 of the quadrupole shape are in the linearly polarized statehaving the polarization direction approximately coincident with acircumferential direction of a circle connecting these four regions 34A,34C, i.e., with a tangential direction to the circle connecting thesefour regions 34A, 34C. FIG. 12B shows the example wherein the secondarylight source 34 of the quadrupole shape is composed of four regions 34A,34C of an almost elliptical shape, but the shape of the four regions isnot limited to the almost elliptical shape.

FIG. 12C shows the secondary light source 35 of a hexapole shape in acase where a diffractive optical element (beam transforming element) forforming a light intensity distribution of a hexapole shape in the farfield (or Fraunhofer diffraction region) is located in the illuminationoptical path, instead of the diffractive optical element 5, and wherethe polarization-modulating element 10 e is located in the illuminationoptical path. Beams passing through the secondary light source 35 of thehexapole shape are set in the azimuthal polarization state. In theazimuthal polarization state, the beams passing through the respectivesix regions 35C, 35F, 35G constituting the secondary light source 35 ofthe hexapole shape are in the linearly polarized state having thepolarization direction approximately coincident with a circumferentialdirection of a circle connecting these six regions 35C, 35F, 35G, i.e.,with a tangential direction to the circle connecting these six regions35C, 35F, 35G. FIG. 12C shows the example wherein the secondary lightsource 35 of the hexapole shape is composed of the four regions 35C,35F, 35G of an almost trapezoidal shape, but the shape of the sixregions is not limited to the almost trapezoidal shape.

The foregoing embodiment and modification example showed thepolarization-modulating elements fixed around the optical axis thereof,but the polarization-modulating element may be arranged rotatable aroundthe optical axis. FIG. 13 is an illustration schematically showing aconfiguration of polarization-modulating element 10 f arranged rotatablearound the optical axis AX.

In FIG. 13, the polarization-modulating element 10 f is composed of acombination of four elementary elements 10A, 10C. Thepolarization-modulating element 10 f has the effective region of anannular shape centered around the optical axis AX as a whole, and thiseffective region of the annular shape is composed of four elementaryelements 10A, 10C of a sector shape as equally divided in thecircumferential direction around the optical axis AX. Among these fourelementary elements 10A, 10C, a pair of elementary elements facing eachother with the optical axis AX in between have the same characteristic.Namely, the four elementary elements 10A, 10C include two types ofelementary elements 10A, 10C two each with mutually differentthicknesses (lengths in the direction of the optical axis) along thedirection of transmission of light (the Y-direction).

The elementary elements 10A are members having the same function as thefirst elementary elements 10A shown in FIG. 7, and the elementaryelements 10C members having the same function as the third elementaryelements 10C shown in FIG. 7. Therefore, the description of thefunctions is omitted herein. A depolarizing member 104 c may be providedin place of the central region 10E.

This-polarization-modulating element 10 f is arranged to be rotatablearound the optical axis AX and, for example, is rotatable by +45° or−45° around the optical axis AX. FIGS. 14A-14C are illustrationsschematically showing examples of the secondary light source set in theazimuthal polarization state by the action of thepolarization-modulating element 10 f. In FIGS. 14A-14C, thepolarization-modulating element 10 f is also illustrated in asuperimposed manner in order to facilitate understanding.

FIG. 14A shows the secondary light source 36 (36A) of a dipole shape ina case where a diffractive optical element (beam transforming element)for forming a light intensity distribution of a dipole shape in the farfield (or Fraunhofer diffraction region) is set in the illuminationoptical path, instead of the diffractive optical element 5, and wherethe polarization-modulating element 10 f is located in a state at therotation angle of 0° (standard state) in the illumination optical path.In this case, beams passing through the secondary light source 36 (36A)of the dipole shape are set in a vertically polarized state.

FIG. 14B shows the secondary light source 37 of a quadrupole shape in acase where a diffractive optical element (beam transforming element) forforming a light intensity distribution of a quadrupole shape in the farfield (or Fraunhofer diffraction region) is located in the illuminationoptical path, instead of the diffractive optical element 5, and wherethe polarization-modulating element 10 f is located in the state at therotation angle of 0° (standard state) in the illumination optical path.In this case, beams passing through the secondary light source 37 of thequadrupole shape are set in the azimuthal polarization state. The lightintensity distribution of the quadrupole shape in FIG. 14B is localizedin the vertical direction (Z-direction) and in the horizontal direction(X-direction) in the plane of the drawing.

In the azimuthal polarization state, beams passing through therespective four circular regions 37A, 37C constituting the secondarylight source 37 of the quadrupole shape are in the linearly polarizedstate having the polarization direction along a circumferentialdirection of a circle connecting these four circular regions 37A, 37C,i.e., with a tangential direction to the circle connecting these fourcircular regions 37A, 37C. FIG. 14B shows the example in which thesecondary light source 37 of the quadrupole shape is composed of thefour circular regions 37A, 37C, but the shape of the four regions is notlimited to the circular shape.

FIG. 14C shows the secondary light source 38 of a quadrupole shape in acase where a diffractive optical element (beam transforming element) forforming a light intensity distribution of a quadrupole shape localizedin the direction of +45° (−135′) in the plane of the drawing and in thedirection of −45° (+135° in the plane of the drawing in the far field(or Fraunhofer diffraction region) is located in the illuminationoptical path, instead of the diffractive optical element shown in FIG.14B, and where the polarization-modulating element 10 f is set in arotated state at the rotation angle of +45° (i.e., in a state in whichit is rotated by 45° clockwise relative to the standard state) in theillumination optical path.

In FIG. 14C, the half wave plate 4 b in the polarization state converter4 is rotated around the optical axis, whereby the linearly polarizedlight having the polarization direction along the direction of +45° (thedirection of −135°) is made incident to the polarization-modulatingelement 10 f. The elementary elements 10A have the function of rotatingthe polarization direction of the incident, linearly polarized light by180°±n×180° (n is an integer), and the elementary elements 10C have thefunction of rotating the polarization direction of the incident,linearly polarized light by 90°±n×180° (n is an integer). Therefore,beams passing through the secondary light source 38 of the quadrupoleshape are set in the azimuthal polarization state.

In the azimuthal polarization state shown in FIG. 14C, beams passingthrough the respective four circular regions 38B, 38D constituting thesecondary light source 38 of the quadrupole shape are in the linearlypolarized state having the polarization direction along acircumferential direction of a circle connecting these four circularregions 38B, 38D, i.e., with a tangential direction to the circleconnecting these four circular regions 38B, 38D. FIG. 14C shows theexample in which the secondary light source 38 of the quadrupole shapeis composed of the four circular regions 38B, 38D, but the shape of thefour regions is not limited to the circular shape.

Through the changing operation of the polarization direction by thepolarization state converter 4 and the rotation operation of thepolarization-modulating element 10 f, as described above, the azimuthalpolarization state can be realized by the secondary light source of thequadrupole shape localized in the +45° (−135° ) direction and in the−45° (+135°) direction, by the secondary light source of the quadrupoleshape localized in the 0° (+180°) direction and in the 90° (270°)direction or in the vertical and horizontal directions, or by thesecondary light source of the dipole shape localized in the 0° (+180°)direction or in the 90° (270°) direction, i.e., in the vertical orhorizontal direction.

The polarization-modulating element composed of the eight elementaryelements of the sector shape as equally divided in the circumferentialdirection around the optical axis AX may be arranged rotatable aroundthe optical axis AX. For example, when the polarization-modulatingelement composed of the eight divisional elementary elements (e.g., thepolarization-modulating element 10 a) is rotated by +45° around theoptical axis AX, as shown in FIG. 15A, the beams passing through therespective eight circular regions 39A-39D constituting the secondarylight source 39 of the octapole shape are in the linearly polarizedstate having the polarization direction resulting from −45° rotationrelative to the circumferential direction of the circle connecting theseeight circular regions 39A-39D (i.e., relative to the tangentialdirection to the circle connecting these eight circular regions39A-39D).

In a case, as shown in FIG. 15B, where the beams passing through therespective eight circular regions constituting the secondary lightsource of the octapole shape are elliptically polarized light having themajor axis along a direction resulting from +45° rotation relative tothe circumferential direction of the circle connecting these eightcircular regions (i.e., relative to the tangential direction to thecircle connecting these eight circular regions), an approximatelyazimuthal polarization state can be achieved, as shown in FIG. 15C, byrotating the polarization-modulating element (e.g.,polarization-modulating element 10 a) by +45° around the optical axis AXas shown in FIG. 15A.

FIG. 16 shows an example in which the polarization-modulating element islocated at a position immediately before the conical axicon system 8(i.e., at a position near the entrance side), among locations near thepupil of the illumination optical apparatus. In this example of FIG. 16,the zoom action of the zoom lens system 9 results in changing the sizeof the image of the central region 10E projected onto the entrancesurface of micro fly's eye lens 11 and the size of the images of therespective elementary elements 10A-10D projected onto the entrancesurface of micro fly's eye lens 11, and the operation of the conicalaxicon system 8 results in changing the width in the radial directionaround the optical axis AX in the images of the respective elementaryelements 10A-10D projected onto the entrance surface of micro fly's eyelens 11.

Therefore, in a case where the polarization-modulating element havingthe central region 10E (or depolarizing member 104 c) is located nearerthe light source than the optical system with the zoom action (zoom lens9) as in the modification example shown in FIG. 16, the size of thecentral region 10E can be determined with consideration to the fact thatthe region occupied by the central region 10E is changed with zooming ofthe zoom lens 9.

In a case where the polarization-modulating element having the centralregion 10E (or depolarizing member 104 c) is located nearer the lightsource than the optical system with the action of changing the annularratio (the conical axicon system 8) as in the modification example shownin FIG. 16, the apparatus is preferably configured to satisfy at leastone of Conditions (1) and (2) below, as shown in FIG. 17.(10 in+ΔA)/10 out<0.75  (1)0.4<(10 in+ΔA)/10 out  (2)The above conditions follow the following notation:

10 in: effective radius of central region 10E of polarization-modulatingelement 10,

10 out: outside effective radius of polarization-modulating element 10,and

ΔA: increase of the inside radius of the beam having passed through theoptical system with the action of changing the annular ratio.

If Condition (1) is not met, the width of the region of the annularshape transformed into the azimuthal polarization state by thepolarization-modulating element 10 will become too small to achieve thecircumferentially polarized illumination based on the secondary lightsource of the annular shape or multipole shape at a small annular ratio;thus it is undesirable. If Condition (2) is not met, the diameter of thebeam passing through the central region of the polarization-modulatingelement 10 will become too small to achieve small-σ illumination withoutchange in the polarization state, for example, unless thepolarization-modulating element 10 is set off the illumination opticalpath; thus it is undesirable.

As shown in FIG. 18, the polarization-modulating element may be locatedat a position nearer the mask than the micro fly's eye lens 11, amonglocations near the pupil of the illumination optical apparatus;specifically, near the pupil position of the imaging optical system 15for projecting the image of mask blind 14 onto the mask. In theembodiments shown in FIG. 16 and in FIG. 18, the plurality ofpolarization-modulating elements may also be arranged replaceable as inthe embodiment in FIGS. 9 to 11.

In the above-described embodiments, if an optical system (theillumination optical system or the projection optical system) nearer thewafer W than the polarization-modulating element 10 has-polarizationaberration (retardation), the polarization direction can vary by virtueof this-polarization aberration. In this case, the direction of theplane of polarization rotated by the polarization-modulating element 10can be set in consideration of the influence of the polarizationaberration of these optical systems. In a case where a reflecting memberis located in the optical path on the wafer W side with respect to thepolarization-modulating element 10, a phase difference can occur betweenpolarization directions of light reflected by this reflecting member. Inthis case, the direction of the plane of polarization rotated by thepolarization-modulating element 10 can be set in consideration of thephase difference of the beam caused by the polarization characteristicof the reflecting surface.

An embodiment of a technique of evaluating the polarization state willbe described below. In the present embodiment, the polarization state ofthe beam arriving at the wafer W as a photosensitive substrate isdetected using a wafer surface polarization monitor 90 which can beattached to a side of a wafer stage (substrate stage) holding the waferW as a photosensitive substrate. The wafer surface polarization monitor90 may be provided in the wafer stage or in a measurement stage separatefrom the wafer stage.

FIG. 19 is an illustration showing a schematic configuration of thewafer surface polarization monitor 90 for detecting the polarizationstate and optical intensity of the light illuminating the wafer W. Asshown in FIG. 19, the wafer surface polarization monitor 90 is providedwith a pinhole member 91 which can be positioned at or near the positionof the wafer W. Light passing through a pinhole 91 a in the pinholemember 91 travels through a collimating lens 92 located so that itsfront focal position is at or near the position of the image plane ofthe projection optical system PL, to become a nearly parallel beam, andthe beam is reflected by a reflector 93 to enter a relay lens system 94.The nearly parallel beam passing through the relay lens system 94travels through a quarter wave plate 95 as a phase shifter and through apolarization beam splitter 96 as a polarizer, and then reaches adetection surface 97 a of two-dimensional CCD 97. The detection surface97 a of two-dimensional CCD 97 is approximately optically conjugate withthe exit pupil of the projection optical system PL and is thusapproximately optically conjugate with the illumination pupil plane ofthe illumination optical apparatus.

The quarter wave plate 95 is arranged rotatable around the optical axisand a setting member 98 for setting the angle of rotation around theoptical axis is connected to this quarter wave plate 95. In thisconfiguration, when the degree of polarization of the illumination lighton the wafer W is not 0, the light intensity distribution on thedetection surface 97 a of two-dimensional CCD 97 varies with rotation ofthe quarter wave plate 95 around the optical axis through the settingmember 98. Therefore, the wafer surface polarization monitor 90 is ableto detect the change in the light intensity distribution on thedetection surface 97 a with rotation of the quarter wave plate 95 aroundthe optical axis by means of the setting member 98 and thereby tomeasure the polarization state of the illumination light from thedetection result by the rotating compensator method.

The rotating compensator method is detailed, for example, in Tsuruta,“Pencil of Light-Applied Optics for optical engineers,” K.K. ShingijutsuCommunications. In practice, the polarization state of the illuminationlight is measured at a plurality of positions on the wafer surface whilethe pinhole member 90 (therefore, pinhole 90 a) is two-dimensionallymoved along the wafer surface. At this time, the wafer surfacepolarization monitor 90 detects a change of the light intensitydistribution on the two-dimensional detection surface 97 a, whereby itcan measure a distribution of polarization states of the illuminationlight in the pupil on the basis of the detected distributioninformation.

The wafer surface polarization monitor 90 can also be configured using ahalf wave plate instead of the quarter wave plate 95 as a phase shifter.With use of any kind of phase shifter, in order to measure thepolarization state, i.e., the four Stokes parameters, it is necessary todetect the change of the light intensity distribution on the detectionsurface 97 a in at least four different states, by changing the relativeangle around the optical axis between the phase shifter and thepolarizer (polarization beam splitter 96) or by moving the phase shifteror the polarizer away from the optical path. The present embodiment isconfigured to rotate the quarter wave plate 95 as a phase shifter aroundthe optical axis, but the polarization beam splitter 96 as a polarizermay be rotated around the optical axis, or both of the phase shifter andthe polarizer may be rotated around the optical axis. Instead of thisoperation, or in addition to this operation, one or both of the quarterwave plate 95 as a phase shifter and the polarization beam splitter 96as a polarizer may be moved into and away from the optical path.

In the wafer surface polarization monitor 90, the polarization state oflight can vary depending upon the polarization characteristic of thereflector 93. In this case, since the polarization characteristic of thereflector 93 is preliminarily known, the polarization state of theillumination light can be accurately measured by compensating themeasurement result of the wafer surface polarization monitor 90 on thebasis of the influence of the polarization characteristic of reflector93 on the polarization state by some calculation. In other cases wherethe polarization state varies due to another optical component such as alens, as well as the reflector, the polarization state of theillumination light can also be accurately measured by compensating themeasurement result in the same manner.

The evaluation for the distribution of polarization states ofillumination light in the pupil will be specifically described below. Adegree of specific polarization DSP is first calculated for each of rayspassing a point (or a microscopic area) on the pupil and arriving at apoint (microscopic area) on the image plane. The XYZ coordinate systemused in FIGS. 1, 16, and 18 will be used in the description hereinafter.The above-described point (microscopic area) on the pupil corresponds toa pixel in the two-dimensional CCD 97, and the point (microscopic area)on the image plane to XY coordinates of the pinhole 90 a.

This degree of specific polarization DSP is represented by the followingequation:DSP=(Ix−Iy)/(Ix+Iy),  (3)where Ix is the intensity of the component of X-directional polarization(polarization with the direction of oscillation along the X-direction onthe pupil) in a specific ray passing a point (or microscopic area) onthe pupil and arriving at a point (microscopic area) on the image plane,and Iy the intensity of the component of Y-directional polarization(polarization with the direction of oscillation along the Y-direction onthe pupil) in the specific ray. This degree of specific polarization DSPis synonymous with horizontal linear polarization intensity minusvertical linear polarization intensity S₁ over total intensity S₀,(S₁/S₀).

We can also define a right polarization rate RSP_(h) for horizontalpolarization (polarization to become S-polarization for diffracted lightby a mask pattern horizontally extending in the pattern surface), and aright polarization rate RSP_(v) for vertical polarization (polarizationto become S-polarization for diffracted light by a mask patternvertically extending in the pattern surface) according to Eqs (4) and(5) below from the intensity 1 x of the component of X-directionalpolarization (polarization with the direction of oscillation along theX-direction on the pupil) in the specific ray passing a point (ormicroscopic area) on the pupil and arriving at a point (microscopicarea) on the image plane and the intensity Iy of the component ofY-directional polarization (polarization with the direction ofoscillation along the Y-direction on the pupil) in the specific ray.RSP _(h) =Ix/(Ix+Iy)  (4)RSP _(v) =Iy/(Ix+Iy)  (5)

RSP_(h) and RSP_(v) both are 50% in ideal unpolarized illumination,RSP_(h) is 100% in ideal horizontal polarization, and RSP_(v) is 100% inideal vertical polarization.

When a polarization degree V is defined by Eqs (6)-(9) below for each ofrays passing a point (or microscopic area) on the pupil and arriving ata point (microscopic area) on the image plane, an average polarizationdegree V(Ave) can be defined as Eq (10) below for a bundle of rayspassing a predetermined effective light source region and arriving at apoint (microscopic area) on the image plane.

$\begin{matrix}\begin{matrix}{V = {( {S_{1}^{2} + S_{2}^{2} + S_{3}^{2}} )^{1\text{/}2}/S_{0}}} \\{= ( {S_{1}^{\prime 2} + S_{2}^{\prime 2} + S_{3}^{\prime 2}} )^{1\text{/}2}}\end{matrix} & (6) \\{S_{1}^{\prime} = {S_{1}/S_{0}}} & (7) \\{S_{2}^{\prime} = {S_{2}/S_{0}}} & (8) \\{S_{3}^{\prime} = {S_{3}/S_{0}}} & (9)\end{matrix}$In the above equations, S₀ represents the total intensity, S₁ horizontallinear polarization intensity minus vertical linear polarizationintensity, S₂ 45° linear polarization intensity minus 135° linearpolarization intensity, and S₃ right-handed circular polarizationintensity minus left-handed circular polarization intensity.V(Ave)=ρ[S ₀(x _(i) ,y _(i))·V(x _(i) ,y _(i))]/ΣS ₀(x _(i) ,y_(i))  (10)

In Eq (10), S₀(x_(i),y_(i)) represents the total intensity S₀ for rayspassing a point (or microscopic area) on a predetermined effective lightsource region (x_(i),y_(i)) and arriving at a point (microscopic area)on the image plane, and V(x_(i),y_(i)) the polarization degree of a raypassing a point (or microscopic area) on the predetermined effectivelight source region (x_(i),y_(i)) and arriving at a point (microscopicarea) on the image plane.

In addition, we can define an average specific polarization rateRSP_(h)(Ave) about horizontal polarization by Eq (11) below and anaverage specific polarization rate RSP_(v)(Ave) about verticalpolarization by Eq (12), for a bundle of rays passing the predeterminedeffective light source region and arriving at a point (microscopic area)on the image plane.

$\begin{matrix}\begin{matrix}{{{RSP}_{h}\;({Ave})} = {{Ix}\;{({Ave})/( {{Ix} + {Iy}} )}\;{Ave}}} \\{= {\sum{\lbrack {{S_{0}( {x_{i},y_{i}} )} \cdot {{RSP}_{h}( {x_{i},y_{i}} )}} \rbrack/{\sum{S_{0}( {x_{i},y_{i}} )}}}}}\end{matrix} & (11) \\\begin{matrix}{{{RSP}_{v}\;({Ave})} = {{Iy}\;{({Ave})/( {{Ix} + {Iy}} )}\;{Ave}}} \\{= {\sum{\lbrack {{S_{0}( {x_{i},y_{i}} )} \cdot {{RSP}_{v}( {x_{i},y_{i}} )}} \rbrack/{\sum{S_{0}( {x_{i},y_{i}} )}}}}}\end{matrix} & (12)\end{matrix}$

Ix(Ave) represents an average intensity of the component ofX-directional polarization (polarization with the direction ofoscillation along the X-direction on the pupil) in a bundle of rayspassing the predetermined effective light source region (x_(i),y_(i))and arriving at a point (microscopic area) on the image plane, Iy(Ave)an average intensity of the component of Y-directional polarization(polarization with the direction of oscillation along the Y-direction onthe pupil) in the bundle of rays passing the predetermined effectivelight source region (x_(i),y_(i)) and arriving at a point (microscopicarea) on the image plane, RSP_(h)(x_(i),y_(i)) a right polarization ratefor horizontal polarization of a ray passing a point (or microscopicarea) on the predetermined effective light source region (x_(i),y_(i))and arriving at a point (microscopic area) on the image plane, andRSP_(v)(x_(i),y_(i)) a right polarization rate for vertical polarizationof a ray passing a point (or microscopic area) on the predeterminedeffective light source region (x_(i),y_(i)) and arriving at a point(microscopic area) on the image plane. In addition, (Ix+Iy)Ave is anaverage intensity of an entire beam passing the predetermined effectivelight source region.

Here, RSP_(h)(x_(i),y_(i)) and RSP_(v)(x_(i),y_(i)) both are 50% inideal unpolarized illumination, RSP_(h)(x_(i),y_(i)) is 100% in idealhorizontal polarization, and RSP_(v)(x_(i),y_(i)) is 100% in idealvertical polarization.

Then we can define an average specific polarization degree DSP(AVE) asEq (13) below, for a bundle of rays passing the predetermined effectivelight source region (x_(i),y_(i)) and arriving at a point (microscopicarea) on the image plane.

$\begin{matrix}\begin{matrix}{{{DSP}\;({Ave})} = {( {{Ix} - {Iy}} )\;{{Ave}/( {{Ix} + {Iy}} )}{Ave}}} \\{= \{ {{\Sigma\lbrack {{{Ix}( {x_{i},y_{i}} )} - {{Iy}( {x_{i},y_{i}} )}} \rbrack}/{\Sigma\lbrack {{{Ix}( {x_{i},y_{i}} )} + {{Iy}( {x_{i},y_{i}} )}} \rbrack}} \}} \\{= {S_{1}^{\prime}({Ave})}} \\{= \{ {\sum{S_{1}/{\sum S_{0}}}} \}}\end{matrix} & (13)\end{matrix}$

Here, (Ix−Iy)Ave represents an average of differences betweenintensities of the X-directional polarization component in a bundle ofrays passing the predetermined effective light source region(x_(i),y_(i)) and arriving at a point (microscopic area) on the imageplane and intensities of the Y-directional polarization component in thebundle of rays passing the predetermined effective light source region(x_(i),y_(i)) and arriving at a point (microscopic area) on the imageplane, Ix(x_(i),y_(i)) the intensity of the X-directional polarizationcomponent in a ray passing a point (or microscopic area) on thepredetermined effective light source region (x_(i),y_(i)) and arrivingat a point (microscopic area) on the image plane, Iy(x_(i),y_(i)) theintensity of the Y-directional polarization component in a ray passing apoint (or microscopic area) on the predetermined effective light sourceregion (x_(i),y_(i)) and arriving at a point (microscopic area) on theimage plane, and S₁′(Ave) an average of the S₁′ component in thepredetermined effective tight source region (x_(i),y_(i)).

In Eq (13), DSP(Ave) becomes 0 in ideal unpolarized DSP(Ave) becomes 1in ideal horizontal polarization, and DSP(Ave) becomes −1 in idealvertical polarization.

In the illumination optical apparatus of the present embodiment and,therefore, in the exposure apparatus, it can be assumed that theinterior of the predetermined effective light source region is linearpolarized light if the average specific polarization rates RSP_(h)(Ave),RSP_(v)(Ave) in the predetermined effective light source region satisfythe following relations:RSP _(h)(Ave)>70%, and RSP _(v)(Ave)>70%.Where the average specific polarization rates RSP_(h)(Ave), RSP_(v)(Ave)fail to satisfy the above conditions, the desired linear polarizationstate with the plane of polarization in the predetermined direction isnot realized in the circumferentially polarized annular illumination,the circumferentially polarized quadrupole illumination, thecircumferentially polarized dipole illumination, and so on, and it isthus infeasible to achieve an improvement in the imaging performance fora pattern with a thin line width having a specific pitch direction.

For example, in a case where the quartered, circumferentially polarizedannular illumination is implemented by use of the quarteredpolarization-modulating element 10 f shown in FIG. 13, the secondarylight source 31 of the annular shape is divided into four segments, asshown in FIG. 20, and the average specific polarization ratesRSP_(h)(Ave), RSP_(v)(Ave) are evaluated for each of the segmentalregions 31A1, 31A2, 31C1, 31C2.

The exposure apparatus according to the foregoing embodiment is able toproduce microdevices (semiconductor elements, image pickup elements,liquid crystal display elements, thin-film magnetic heads, etc.) byilluminating a mask (reticle) by the illumination optical apparatus(illumination step) and projecting a pattern for transcription formed onthe mask, onto a photosensitive substrate by use of the projectionoptical system (exposure step). The following will describe an exampleof a procedure of producing semiconductor devices as microdevices byforming a predetermined circuit pattern on a wafer or the like as aphotosensitive substrate by means of the exposure apparatus of theforegoing embodiment, with reference to the flowchart of FIG. 9.

The first step 301 in FIG. 9 is to deposit a metal film on each ofwafers in one lot. The next step 302 is to apply a photoresist onto themetal film on each wafer in the lot. Thereafter, step 303 is tosequentially transcribe an image of a pattern on a mask into each shotarea on each wafer in the lot, through the projection optical system byuse of the exposure apparatus of the foregoing embodiment. Subsequently,step 304 is to perform development of the photoresist on each wafer inthe lot, and step 305 thereafter is to perform etching with the resistpattern as a mask on each wafer in the lot, thereby forming a circuitpattern corresponding to the pattern on the mask, in each shot area oneach wafer. Thereafter, devices such as semiconductor elements areproduced through execution of formation of circuit patterns in upperlayers and others. The semiconductor device production method asdescribed above permits us to produce the semiconductor devices withextremely fine circuit patterns at high throughput.

The exposure apparatus of the foregoing embodiment can also be appliedto production of a liquid crystal display element as a microdevice insuch a manner that predetermined patterns (a circuit pattern, anelectrode pattern, etc.) are formed on a plate (glass substrate). Anexample of a procedure of this production will be described below withreference to the flowchart of FIG. 10. In FIG. 10, pattern forming step401 is to execute a so-called photolithography step of transcribing apattern on a mask onto a photosensitive substrate (a glass substratecoated with a resist or the like) by use of the exposure apparatus ofthe foregoing embodiment. In this photolithography step, thepredetermined patterns including a number of electrodes and others areformed on the photosensitive substrate. Thereafter, the exposedsubstrate is subjected to steps such as a development step, an etchingstep, a resist removing step, etc., to form the predetermined patternson the substrate, followed by next color filter forming step 402.

The next color filter forming step 402 is to form a color filter inwhich a number of sets of three dots corresponding to R (Red), G(Green), and B (Blue) are arrayed in a matrix, or in which a pluralityof sets of filters of three stripes of R, G, and B are arrayed in thedirection of horizontal scan lines. After the color filter forming step402, cell assembly step 403 is carried out. The cell assembly step 403is to assemble a liquid crystal panel (liquid crystal cell), using thesubstrate with the predetermined patterns obtained in the patternforming step 401, the color filter obtained in the color filter formingstep 402, and so on.

In the cell assembly step 403, for example, a liquid crystal is pouredinto the space between the substrate with the predetermined patternsobtained in the pattern totaling step 401 and the color filter obtainedin the color filter forming step 402 to produce the liquid crystal panel(liquid crystal cell). Thereafter, module assembly step 404 is carriedout to attach such components as an electric circuit, a backlight, andso on for implementing the display operation of the assembled liquidcrystal panel (liquid crystal cell), to complete the liquid crystaldisplay element. The production method of the liquid crystal displayelement described above permits us to produce the liquid crystal displayelements with extremely fine circuit patterns at high throughput.

The foregoing embodiment is arranged to use the KrF excimer laser light(wavelength: 248 nm) or the ArF excimer laser light (wavelength: 193 nm)as the exposure light, but, without having to be limited to this, thepresent invention can also be applied to other appropriate laser lightsources, e.g., an F₂ laser light source for supplying laser light of thewavelength of 157 nm. Furthermore, the foregoing embodiment describedthe present invention, using the exposure apparatus with theillumination optical apparatus as an example, but it is apparent thatthe present invention can be applied to ordinary illumination opticalapparatus for illuminating the surface to be illuminated, except for themask and wafer.

In the foregoing embodiment, it is also possible to apply the so-calledliquid immersion method, which is a technique of filling a medium(typically, a liquid) with a refractive index larger than 1.1 in theoptical path between the projection optical system and thephotosensitive substrate. In this case, the technique of filling theliquid in the optical path between the projection optical system and thephotosensitive substrate can be selected from the technique of locallyfilling the liquid as disclosed in PCT International Publication No.WO99/49504, the technique of moving a stage holding a substrate as anexposure target in a liquid bath as disclosed in Japanese PatentApplication Laid-Open No. 6-124873, the technique of forming a liquidbath in a predetermined depth on a stage and holding the substratetherein as disclosed in Japanese Patent Application Laid-Open No.10-303114, and so on.

The liquid is preferably one that is transparent to the exposure light,that has the refractive index as high as possible, and that is stableagainst the projection optical system and the photoresist applied to thesurface of the substrate; for example, where the exposure light is theKrF excimer laser light or the ArF excimer laser light, pure water ordeionized water can be used as the liquid. Where the F₂ laser light isused as the exposure light, the liquid can be a fluorinated liquidcapable of transmitting the F₂ laser light, e.g., fluorinated oil orperfluoropolyether (PFPE).

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

What is claimed is:
 1. An illumination optical apparatus whichilluminates an object having a pattern with illumination light, theillumination optical apparatus comprising: an optical integratorarranged in an optical path of the illumination light; and apolarization modulating member made of an optical material with opticalactivity, the polarization modulating member having a thickness thatvaries with respect to azimuthal positions about an optical axis of theillumination optical apparatus, the polarization modulating member beingarranged in the optical path on an incidence side of the opticalintegrator and being arranged around the optical axis so as to surroundthe optical axis, a direction of an optic axis of the optical materialbeing substantially coincident with a direction of the optical axis ofthe illumination optical apparatus, wherein the polarization modulatingmember rotates a polarization direction of the illumination light sothat the illumination light, being incident on the polarizationmodulating member in a linearly polarized state having the polarizationdirection along a single direction, is changed to a linearly polarizedstate having polarization directions being substantially coincident withan azimuthal direction about the optical axis at a pupil plane of theillumination optical apparatus, wherein the polarization modulatingmember has a region without optical activity in an area perpendicular tothe optical axis, the region being on the optical axis, and wherein thepolarization modulating member has substantially constant thicknesses inat least two radial directions that are not parallel to each other. 2.The illumination optical apparatus according to claim 1, wherein theillumination light is irradiated onto the object in a polarization statein which a principal component is S-polarized light.
 3. The illuminationoptical apparatus according to claim 1, wherein a first thickness of thepolarization modulating member in an optical path of a first part of theillumination light is different from a second thickness of thepolarization modulating member in an optical path of a second part ofthe illumination light, and the first part of the illumination lightpasses through a first portion of the pupil plane away from the opticalaxis, and the second part of the illumination light passes through asecond portion of the pupil plane away from the optical axis, the firstand second portions being different from each other.
 4. The illuminationoptical apparatus according to claim 3, further comprising apolarization converter arranged in the optical path on an incidence sideof the polarization modulating member, wherein the polarizationconverter converts a polarization state of the illumination light from afirst polarization state including a substantially single polarizationinto a second polarization state different from the first polarizationstate.
 5. The illumination optical apparatus according to claim 4,wherein a principal component of the second polarization state islinearly polarized light polarized substantially in the singledirection.
 6. The illumination optical apparatus according to claim 4,wherein a principal component of the first polarization state islinearly polarized light, circularly polarized light or ellipticallypolarized light.
 7. The illumination optical apparatus according toclaim 4, wherein the polarization converter comprises at least one of ahalf wavelength plate and a quarter wavelength plate.
 8. Theillumination optical apparatus according to claim 4, wherein the firstand second portions are included in an annular region about the opticalaxis.
 9. The illumination optical apparatus according to claim 8,wherein the first and second portions are substantially discrete fromeach other.
 10. The illumination optical apparatus according to claim 4,wherein the first and second portions are substantially discrete fromeach other and are aligned along a circumference about the optical axis.11. The illumination optical apparatus according to claim 3, wherein thefirst and second portions are included in an annular region about theoptical axis.
 12. The illumination optical apparatus according to claim11, wherein the first and second portions are substantially discretefrom each other.
 13. The illumination optical apparatus according toclaim 3, wherein the first and second portions are substantiallydiscrete from each other and are aligned along a circumference about theoptical axis.
 14. The illumination optical apparatus according to claim1, wherein the optical integrator comprises a fly's eye lens, and asurface of an exit side of the fly's eye lens is arranged at a positionsubstantially equivalent to the pupil plane.
 15. The illuminationoptical apparatus according to claim 1, further comprising apolarization converter arranged in the optical path on an incidence sideof the polarization modulating member, wherein the polarizationconverter converts a polarization state of the illumination light from afirst polarization state including a substantially single polarizationinto a second polarization state different from the first polarizationstate.
 16. The illumination optical apparatus according to claim 15,wherein a principal component of the second polarization state islinearly polarized light polarized substantially in the singledirection.
 17. The illumination optical apparatus according to claim 15,wherein a principal component of the first polarization state islinearly polarized light, circularly polarized light or ellipticallypolarized light.
 18. The illumination optical apparatus according toclaim 15, wherein the polarization converter comprises at least one of ahalf wavelength plate and a quarter wavelength plate.
 19. An exposuremethod which exposes a substrate to light via an object having apattern, the exposure method comprising: holding the substrate by thestage; illuminating the pattern with the light by using the illuminationoptical apparatus as defined in claim 1; and projecting an image of thepattern illuminated with the light onto the substrate held by the stage.20. The exposure method according to claim 19, wherein the substrate isexposed to the light through liquid.
 21. A device manufacturing method,comprising: transferring a pattern to a substrate by using the exposuremethod as defined in claim 19; and developing the substrate to which thepattern is transferred.
 22. An exposure apparatus which exposes asubstrate to light via an object having a pattern, the exposureapparatus comprising: a stage which holds the substrate, theillumination optical apparatus as defined in claim 1 which illuminatesthe pattern with the light; and a projection optical system whichprojects an image of the pattern illuminated with the light onto thesubstrate held by the stage, wherein the polarization modulating memberhas a region without optical activity in an area perpendicular to theoptical axis, the region being on the optical axis, and wherein thepolarization modulating member has substantially constant thicknesses inat least two radial directions that are not parallel to each other. 23.The exposure apparatus according to claim 22, wherein the substrate isexposed to the light through liquid.
 24. The exposure apparatusaccording to claim 22, wherein the light is irradiated onto the objectin a polarization state in which a principal component is S-polarizedlight.
 25. The exposure apparatus according to claim 22, wherein a firstthickness of the polarization modulating member in an optical path of afirst part of the light is different from a second thickness of thepolarization modulating member in an optical path of a second part ofthe light, and the first part of the light passes through a firstportion of the pupil plane away from the optical axis, and the secondpart of the light passes through a second portion of the pupil planeaway from the optical axis, the first and second portions beingdifferent from each other.
 26. The exposure apparatus according to claim25, further comprising a polarization converter arranged in the opticalpath on an incidence side of the polarization modulating member, whereinthe polarization converter converts a polarization state of the lightfrom a first polarization state including a substantially singlepolarization into a second polarization state different from the firstpolarization state.
 27. The exposure apparatus according to claim 26,wherein a principal component of the second polarization state islinearly polarized light polarized substantially in the singledirection.
 28. The exposure apparatus according to claim 26, wherein aprincipal component of the first polarization state is linearlypolarized light, circularly polarized light or elliptically polarizedlight.
 29. The exposure apparatus according to claim 26, wherein thepolarization converter comprises at least one of a half wavelength plateand a quarter wavelength plate.
 30. The exposure apparatus according toclaim 25, wherein the first and second portions are included in anannular region about the optical axis.
 31. The exposure apparatusaccording to claim 30, wherein the first and second portions aresubstantially discrete from each other.
 32. The exposure apparatusaccording to claim 25, wherein the first and second portions aresubstantially discrete from each other and are aligned along acircumference about the optical axis.
 33. The exposure apparatusaccording to claim 22, wherein the optical integrator comprises a fly'seye lens, and a surface of an exit side of the fly's eye lens isarranged at a position substantially equivalent to the pupil plane. 34.A device manufacturing method, comprising: transferring a pattern to asubstrate by using the exposure apparatus as defined in claim 22; anddeveloping the substrate to which the pattern is transferred.